Gaining an in-depth understanding is the main challenge for fast and successful development and implementation of a bioprocess. In past years, microdevices became an attractive tool to scale down, develop and optimize bioprocesses. Microfluidic devices provide new methodologies to simulate bioprocesses by controlling the fluid conditions on small scale and generating data in a high-throughput manner. To design and develop microfluidic devices, computational fluid dynamics (CFD) is a valuable methodology to predict fluid flows, mixing behavior and other hydrodynamic phenomena. Microfluidics are characterized by small channels with controllable laminar flows. However, several bioprocesses require turbulent flows for fast and homogeneous mixing. To down-scale such processes, active mixers are being implemented in microfluidic devices, but there is limited information on how fluids behave in microdevices when external turbulences are applied. CFD can be used to study flow behavior in microfluidic systems and can predict mixing times, shear rates, distribution of nutrients and distribution of oxygen in micro-bioreactors.